AssemblyAI Ships AssemblyAI-TTS-1: A $15 per 1M Character Text-to-Speech API for Voice Agents

AssemblyAI has released AssemblyAI-TTS-1 , its first text-to-speech model, now generally available. The AssemblyAI-TTS-1 text-to-speech API targets voice agents running on live phone calls. In that setting, latency and pronunciation decide whether a caller stays on the line. Pricing is $15 per 1M characters , with no annual contract and no concurrency tier to buy. For developers already using AssemblyAI speech-to-text, it closes the voice loop with one vendor. TL;DR Size: It is a hosted API model. Runs on: AssemblyAI’s cloud only, in the US (us-east-1) or EU (eu-north-1) . No open weights or on-prem option. Any client with HTTP or WebSocket works. Performance: Ties ElevenLabs v4 on entity accuracy in AssemblyAI’s tests, at under 1/5 of its price. Best: 47 ms median time to first byte across 6 models in AssemblyAI’s API test (self-reported). Worst: 159 ms median streaming latency on Cekura’s independent benchmark , 8th of 19 timed models. Bottom line: Best: $15 per 1M characters with unlimited concurrency. Worst: no SSML, speed control, pronunciation dictionaries or emotion tags yet. What is AssemblyAI-TTS-1? AssemblyAI-TTS-1 is a streaming text-to-speech model from AssemblyAI that turns agent replies into speech for live calls. It was trained on millions of hours of audio , including real conversational data. Most TTS models represent audio as discrete tokens. AssemblyAI says TTS-1 operates on continuous audio representations instead. The AssemblyAI claims this improves realism and cuts time to first spoken audio. The launch includes a library of 4,000+ voices and instant voice cloning. A clone needs a short recording and a confirmation of the speaker’s permission. The clone in the launch post used 24 seconds of audio. Six languages are supported at launch: English, Spanish, French, German, Italian and Portuguese. How do developers integrate AssemblyAI-TTS-1? There are 3 interfaces: an HTTP API, a WebSocket API and an OpenAI-compatible route . The WebSocket session keeps one connection per conversation and accepts a cancel message for barge-in. Output is mono PCM, mu-law or A-law, at 8 kHz to 48 kHz. 24 kHz PCM is the native format; telephony stacks can request 8 kHz mu-law directly. Word timestamps are included. AssemblyAI also published LiveKit and Pipecat reference agents. How does AssemblyAI-TTS-1 perform on benchmarks? AssemblyAI tested TTS-1 against 5 models on 4 English sets, using 50 matched cloned voices. All figures below are self-reported , from an eval dated October 28, 2026. Entity accuracy (580 hard targets such as phone numbers and codes): 93.7%, vs ElevenLabs v4 93.6%, Cartesia Sonic 3.6 82.5%, ElevenLabs Flash v2.5 68.0%. Word accuracy: 99.0% on Seed-TTS and LibriSpeech sentences. Predicted MOS: 3.85, behind Inworld TTS-2 Flash at 3.88 and ahead of Sonic 3.6 at 3.82. Median time to first byte: 47 ms. Flash v2.5 took 119 ms, Sonic 3.6 143 ms, Inworld TTS-2 Flash 244 ms. Other: 85.5 TTSDS prosody score and 0.64 speaker similarity for cloned audio. Independent results are more mixed. On Cekura’s benchmark of 27 models, TTS-1 scored 81.5% reading accuracy and 4.50 naturalness. Its median streaming latency, timed from the last word sent, was 159 ms. Inworld TTS-2 Flash posted 45 ms and 93.2% accuracy there, at the same $15 price. AssemblyAI also cites a 1.7% word error rate on Coval’s leaderboard . It reports a top-10 debut in Artificial Analysis’ controlled-voice arena. Play</button> <button class="btn ghost" id="aai-prev">‹ Back</button> <button class="btn ghost" id="aai-next">Next ›</button> </div> </div> <div class="pane" data-p="bench"> <div class="pills" id="aai-pills"> <button class="pill on" data-m="ent">Entity accuracy</button> <button class="pill" data-m="ttfb">Median TTFB (AssemblyAI test)</button> <button class="pill" data-m="cstream">Streaming latency (Cekura)</button> <button class="pill" data-m="cacc">Reading accuracy (Cekura)</button> </div> <div class="bars" id="aai-bars"></div> <p class="note" id="aai-bnote"></p> </div> <div class="pane" data-p="cost"> <div class="calc"> <label for="aai-min">Spoken minutes per month: <b id="aai-minv" style="color:#fdfcf8">10,000</b></label> <input type="range" id="aai-min" min="1000" max="200000" step="1000" value="10000"> <div class="cost" id="aai-cost"></div> <p class="note">Assumes 600 characters per minute of phone speech, the figure AssemblyAI cites as typical. List prices per 1M characters: AssemblyAI-TTS-1 $15, Inworld TTS-2 Flash $15 on demand, ElevenLabs Flash v2.5 $40, ElevenLabs v4 $80. Concurrency limits are not priced in.</p> </div> </div> <div class="pane" data-p="limits"> <div class="grid" id="aai-cards"> <div class="card"><h4>No SSML or speed control <span class="tag">LAUNCH GAP</span></h4><p>The WebSocket API has no speed, pitch, emotion or style parameter, and neither API accepts SSML. Punctuation and written fillers like "um" still shape delivery.</p></div> <div class="card"><h4>No pronunciation dictionaries <span class="tag">COMING SOON</span></h4><p>Custom pronunciation dictionaries and emotion tags are announced but not shipped. Cartesia Sonic 3.6 already offers custom pronunciations.</p></div> <div class="card"><h4>6 languages <span class="tag">COVERAGE</span></h4><p>English, Spanish, French, German, Italian and Portuguese. ElevenLabs Flash v2.5 lists 32 and Cartesia Sonic 3.6 lists 44.</p></div> <div class="card"><h4>Latency depends on method <span class="tag">CHECK IT</span></h4><p>About 90 ms advertised, 47 ms median in AssemblyAI's own test, 159 ms median streaming latency on Cekura (timed from the last word sent).</p></div> <div class="card"><h4>Instant cloning only <span class="tag">LAUNCH GAP</span></h4><p>Pro (fine-tuned) voice cloning is not available yet. Instant clones need a short clip and speaker permission.</p></div> <div class="card"><h4>Cloud only <span class="tag">DEPLOYMENT</span></h4><p>US (us-east-1) and EU (eu-north-1) hosts at the same price. No on-prem option is announced.</p></div> </div> <p class="note">Tap a card to expand it.</p> </div> <div class="ft"><span>Sources: AssemblyAI launch post, docs and pricing; Cekura TTS benchmark; vendor pricing pages. 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